Update XP-Pen report parser

[X9VoiD]

Changes

• Support 8 buttons
• Use BitVector32 wherever profitable
• Simplify aux report detection
  • Remove redundant check on XP_PenAuxReport (already performed in XP_PenReportParser)
• Skip BitConverter's unneeded safety checks by directly calling Unsafe.ReadUnaligned<T>()

  We know in advance that the bytes we're parsing are complete

[InfinityGhost]

If there is actually tangible evidence this improves performance, this could be applied to other report parsers as well.

[InfinityGhost]

Worth the change, we should go ahead and make these changes to other report parsers while we're at it, ideally in separate branches so we can merge on a per-manufacturer basis.